Objective To establish an objective endpoint criterion for the nine cycles of steaming and sun-drying in the processing of Shudihuɑng (Rehmanniae Radix Praeparata, RRP), to quantitatively characterize the dynamic changes in “morphology, color, and taste”, and to elucidate the correlation between chemical component transformations and the Maillard reaction. Methods Samples subjected to one through nine cycles of conventional steaming and wine-assisted steaming were prepared. An integrated analytical approach combining electronic tongue, electronic nose, electronic eye, mass spectrometry imaging, and infrared spectroscopy was employed to obtain quantitative parameters related to taste, odor, and chromaticity. These data were used to analyze the spatial distribution and dynamic variation of chemical constituents, as well as the migration patterns of characteristic functional groups. Results The electronic sensory data exhibited strong concordance with the results of manual sensory evaluation and demonstrated high discriminative capability among RRP samples subjected to varying cycles of re-hydration and re-drying. A pronounced shift in taste profile was observed at the third cycle of re-hydration and re-drying, identified as the critical inflection point for sensory deterioration. Concurrently, the color value decreased progressively with increasing reprocessing cycles—a trend consistent with the traditional quality benchmark “black as lacquer, sweet as honey”, wherein darker coloration correlates with superior quality. Volatile propane-type compounds were identified as key odor discriminants across treatment groups. Mass spectrometry imaging revealed that with increasing processing intensity, the levels of iridoid compounds, amino acids, and non-reducing sugars progressively declined, whereas those of reducing sugars and 5-hydroxymethylfurfural increased steadily. In contrast, phenethyl alcohol exhibited a triphasic trend—initially increasing, subsequently decreasing, and finally rising again. Fourier-transform infrared (FTIR) spectroscopy further demonstrated characteristic shifts in absorption peaks corresponding to sugar-derived hydroxyl groups and conjugated carbonyl moieties, consistent with hallmark spectral features of the Maillard reaction. Notably, organic acids present in the wine-steaming medium exerted a catalytic effect, advancing the onset of quality inflection points by one steaming cycle relative to the clear-steaming control group; However, no statistically significant difference in final product quality was observed between the two processing modalities. Conclusion The proposed multi-dimensional evaluation system objectively captures the evolutionary patterns of “morphology, color, and taste” throughout the nine-cycle steaming and sun-drying process of processed RRP. These findings provide a quantitative foundation for determining the optimal processing endpoint and offer a technical framework for quality control in the production of steamed and sun-dried traditional Chinese medicines.

Rehmanniae Radix Praeparata  /  nine steamed and nine sun-dried  /  electronic tongue  /  electronic nose  /  electronic eye  /  mass spectrometry imaging  /  infrared spectroscopy